Zinc Oxide Quantum Dots Array for Cortisol Sensing via Aptamer‐Antibody Sandwich Assay

ABSTRACT This study presents a proof‐of‐concept cortisol sensing array via lithographically patterned zinc oxide (ZnO) quantum dot (QD) arrays coupled with 2 nm gold nanoparticles (AuNPs) through aptamer‐antibody sandwich (AAS) architecture. Ultrathin (∼35 nm) circular ZnO QD patterns were fabricated by colloidal photolithography using acrylate precursor followed by surface modification for subsequent bioconjugation. Cortisol specific binding aptamers (cSBA) as primary probe were immobilized on photostable ZnO QDs, while cortisol monoclonal antibody (cMab) conjugated 2 nm AuNPs has served as secondary probe for localized surface plasmon resonance (LSPR) and photoluminescence (PL) assay simultaneously. In LSPR mode, redshift of ZnO band‐edge absorbance from 358 to 370 nm could be induced along with a concurrent absorbance decrease. In PL quench mode, interband absorption of 2 nm AuNPs partially overlaps with broad ZnO QD defect emission band (45 –700 nm) providing fluorescence resonance energy transfer (FRET) effect. PL spectra exhibited reshaping with quenched peaks near 605 nm and at 655 and 678 nm. Moreover, direct optical detection method can have a high sensitivity with limit of cortisol detection of 0.1 n m . The developed AAS‐based array demonstrates great potential as a rapid and precise diagnostic tool in advanced point‐of‐care testing (POCT) systems.